This invention relates generally to gas-insulated equipment, and more particularly to a gas-filled bushing using an increased diameter conductor portion at the end of the bushing to minimize the throat diameter thereof.
Gas-insulated equipment is being used on ever-increasing scale in recent years due to the desirability of increasing safety, problems in acquiring the necessary acreage for substations and right-of-way for overhead lines, higher power requirements of growing metropolitan areas, and the overall growing demands for electrical energy. Typical of such installations are gas-insulated, high voltage substations dealing with voltages of magnitudes in the kilovolt ranges and higher, with main components such as circuit breakers, switches, capacitor banks, and the like, enclosed in gas-filled grounded metal containers which are interconnected by elongated conductors which are also contained in outer grounded sheaths filled with the insulating gas. Typical of the gas utilized in these substations is sulfur hexafluoride, whose high dielectric strength minimizes the separation distances required between adjacent electrical components, to thereby decrease the size of the equipment.
Generally, whenever utilizing gas-insulated equipment, it is necessary to provide an air entrance bushing to make the connection from an overhead line, for example, to the gas-insulated equipment. Presently, these bushings generally consist of an elongated porcelain or epoxy body of tapering or straight diameter with suitable corona rings at the ends of the body to allow adequate flaring of dielectric potential lines.
For certain applications, as for example a compact, gas-insulated capacitor bank, the sulfur hexafluoride gas is utilized at a low pressure, for example 10 pounds per square inch gauge. At these low pressures, the throat diameter of a gas-insulating bushing can become very large for the most economical choice of conductor. That is, if the conductor diameter is sized to carry a given rated current and is dimensioned accordingly, with a small diameter conductor, the throat diameter of the insulating shell of the bushing can correspondingly be very large. The increase in size of this throat diameter of the shell is directly translatable into a higher cost to produce the shell. It therefore is desirable to achieve some means of decreasing the size of the throat diameter of the insulating shell, thereby reducing the manufacturing cost for the shell, without incurring the penalty associated with increasing the conductor size.